Structural Deflection and Load Measuring Device

ABSTRACT

The present invention provides a structural deflection and load measuring device for mounting on an axle. The device includes at least one light beam emitting device connected to the axle and able to emit at least one light beam and at least one light position sensing device connected to the axle. The sensing device is located relative to the light beam emitting device for receiving at least one light beam from the light beam emitting device thereon and is operable to calculate the position of the light beam received on its surface.

FIELD OF THE INVENTION

The present invention provides a means for measuring the bending/sheardeflection of a structure, and through knowledge of the type ofstructure, provides means to determine the loads/forces applied to thestructure. The present invention provides means for measuring structuraldeflections in general, and axle deflections in particular. Moreparticularly, the present invention provides means to measure thedeflections of aircraft landing gear axles and for determining the loadsapplied thereto.

BACKGROUND OF THE INVENTION

An axle is generally described as a supporting shaft for a rotatingwheel(s) or gear(s). Axles are used in many different environments,including in automobiles and aircraft. In general use, an axle may berequired to sustain varying weights placed upon it and therefore itsstructural integrity may be important to its lifespan. For example, inan aircraft application there will be an increase in the load placed onthe axle when the plane is stationary and being loaded with passengers,cargo and fuel. An even greater load will be placed on the axle when thewheels and the axle to which they are attached come into contact withthe runway upon landing. It is therefore desirable to monitor thecondition of the axle to ensure that it is not damaged or in need ofservicing or maintenance.

Knowing the forces applied to aircraft landing gear axles provides forthe determination of aircraft weight and balance, which is of interestto aircraft operators. The weight (mass of the aircraft, fuel,occupants, and cargo) and balance (the position of the centre of gravityof the aircraft) are critical factors that require measurement orcalculation prior to every flight. Currently, almost every aircraftdeparts using calculated weight and balance values. These calculatedvalues are based on average weights, not the actual weights ofpassengers and baggage, so aircraft operators must limit the usage oftheir aircraft to a narrower band of weight and balance values than thatset by the aircraft manufacturer. This limits the utilisation of theaircraft, and reduces its potential revenue. In addition, thecalculations are performed manually in some instances, and in others bycentral calculation departments. If a method of measuring the weight andcentre of gravity existed that could reliably determine these values,the usage of the aircraft would increase (more passengers/cargo) couldbe carried, and the costs to aircraft operators to determine the valuescould be significantly reduced.

A number of attempts to determine the weight of aircraft have beentried, with various degrees of success. The benchmark are stationaryscales that an aircraft rolls onto, such that each landing gear orlanding gear wheel is weighed. This method provides the standard towhich all others are compared, but since the scales are not carriedaboard the aircraft, and since the weighing procedure typically takes asignificant amount of time, this method is not appropriate for thedetermination of the aircraft weight and balance prior to each flight. Anumber of flyable approaches have been attempted. In all these methodsthe landing gear, or portions thereof, form the element on which themeasurement will be made since the landing gear, and its associatedwheels and tires, are where the aircraft's weight is reacted by theground. One of the earliest approaches to determining the weight over alanding gear was by measuring the pressure of the gas in the gas springthat supports the aircraft. This method suffers from a lack of accuracydue to the friction of the gas and oil seals in the strut which carrysome of the load. Methods exist (Nance) to account for this friction,but these are either based on empirical data or require complicating thegas oil strut of the landing gear with various valves, tubes, andactuators that by their existence reduce the reliability of the landinggear system.

Other methods have been tried that more directly relate to the presentinvention—they work by attempting to measure the deflection of thelanding gear axles. A direct approach uses strain gauges, either bondedto the axle, or bonded to a sensor fitted within the axle. Strain gaugesuse conductive metal that when stretched or compressed will cause anincrease or decrease in electrical resistance across the material. Theamount of change in the electrical resistance can be used as ameasurement of the strain or deflection that the component to which thestrain gauge is attached to is under. Such gauges have limitations basedon the constriction of the elastic limits of the material used and thelack of high accuracy that can occur in the measurement readings. Inaddition, strain gauged based systems suffer from a lack of longevity inlanding gear applications related to their reliance on mechanicalbonding (gluing) of the gauge to the area of interest. Another point offailure of strain gauges is through corrosion where the electrical leadsare terminated to the gauge. These terminations are by necessity in aharsh environment (the aircraft landing gear axle) and typically do notsurvive long in service.

A further attempt to measure the shear deflection of the axle has beenfielded. This system employs a variable reluctance sensor which operatesby measuring directly the displacement of the landing gear axle. Thesensor is bolted to specially machined lugs on the exterior of thelanding gear axle. In practice the system is expensive due to therequirement for machining lugs on a part which would be normally havebeen turned in a lathe and difficult to calibrate and use.

Other systems, which have been contemplated or demonstrated, includesystems that directly measure material properties of a component towhich they are attached, i.e. the axle. Such measurements (such asBarkhausen noise and other magnetic domain measurements) are thencompared to predetermined material measurements and can be used todetermine any potential stress on the component material. Many of thesesystems are experimental and have not had their reliability proven. Inaddition, there are questions as to how certain material properties ofinterest to these sensors change naturally with time. For instance, theBarkhausen noise properties of steel may change naturally over the lifeof a landing gear, confounding the original calibration.

In addition to the interest in measuring the weight of an aircraft, itis of interest to measure the forces acting on a landing gear in orderto better determine the structural life and integrity of said landinggear. A method to measure axle deflections could provide a significantamount of information towards the determination of landing gearstructural life.

SUMMARY OF THE INVENTION

The present invention provides a structural deflection and loadmeasuring device for mounting on an axle comprising at least one lightbeam emitting device connected to the axle and operable to emit at leastone light beam and at least one light position sensing device connectedto the axle and located relative to the light beam emitting device. Theat least one light position sensing device comprising at least twoindependent locations for receiving an incident beam and operable tomeasure the at least two independent locations. The at least twoindependent locations may be located on the same or different lightposition sensing devices.

The present invention further provides a refractive optical devicelocated between the at least one light position sensing device and theat least one light emitting device and within the path of the light beamfor refracting the light beam prior to being received on the lightposition sensing device.

The present invention further provides a device that includes at leastone light beam emitting device and at least one light position sensingdevice being located proximal to each other, for example within the sameplane, and a reflective optical device which is located at a positiondistal from the at least one light beam emitting device and the at leastone light position sensing device and positioned to reflect the beamemitted from the at least one emitting device onto the at least oneposition sensing device.

The present invention further provides a housing to contain thestructural deflection and load measuring device described herein and formounting on or within an axle.

The present invention further provides a structural deflection and loadmeasuring device comprising a first light beam emitting device operableto emit at least one light beam and a first light position sensingdevice for receiving the first light beam and a second light beamemitting device operable to emit at least one light beam and a secondlight position sensing device located relative to the second light beamemitting device for receiving at least one light beam emitted from thesecond light beam emitting device thereon. The device further comprisesa refractive optical device located between the second light emittingdevice and the second light position sensing device for enhancing thedeflection of the second light beam.

The present invention further provides transmitting means connected tothe at least one light position sensing device for transmitting themeasured locations of the light beam. Preferably the device alsocomprises a processor which is connected to the transmitting means andoperable to calculate at least one of weight, balance and load of theaircraft using the measured location(s) of the light beam.

The present invention further comprises a method for measuring axledeflection using an optical axle deflection sensor comprising at leastone light emitting device connected to the axle and at least one lightposition sensing device connected to the axle and located relative tothe light beam emitting device for receiving at least one light beamfrom the light beam emitting device thereon, the method comprising thesteps of (i) measuring the position of the light beam from the lightbeam emitting device on the light position sensing device when no loadis applied to the axle (ii) applying a load to the axle and re-measuringthe position of the light beam on the sensing device (iii) comparing theposition of the light beam in (i) with (ii) and calculating the lightbeam deflection; and (iv) calculating the axle deflection using thelight beam deflection calculated in (iii). The method further comprisesusing the calculated axle deflection of step (iv) to determine at leastone of weight, balance and load on the axle.

The present invention further comprises a structural deflection and loadmeasuring device for mounting on a dual wheel axle comprising a housingfor mounting on the axle; at least one mirror assembly for mounting onthe inside of at least one wheel hub cap connected to the wheel axle, atleast one light beam emitting device contained within the housing andoperable to emit at least one light beam towards the mirror assembly andat least one light position sensing device contained within the housingand located adjacent the light beam emitting device for receiving the atleast one deflected light beam from the mirror assembly thereon andoperable to calculate the position of the light beam received thereon.

The present invention further provides a mirror assembly comprising aplurality of light absorbing elements. The light absorbing elements maybe radially extending elements, for example radially extending stripes.The mirror assembly may include at least one mirror and at least one ofa reflective lens and a refractive lens.

The present invention further provides a system for measuring theweight, balance and/or load of an aircraft comprising at least onestructural deflection and load measuring device described herein locatedon each axle of the aircraft. The present invention further provides asystem for measuring the weight, balance and/or load of an aircraftincluding additional structural deflection and load measuring devicesmounted at predetermined positions on the aircraft landing gear, forexample on a bogie beam.

The present invention further provides a structural deflection and loadmeasuring device for mounting on an axle comprising a housing formounting on the axle a first light beam emitting device contained withinthe housing and operable to emit at least one light beam, a first lightposition sensing device contained within the housing and locatedrelative to the light beam emitting device for receiving at least onelight beam from the first light beam emitting device thereon andoperable to calculate the position of the light beam received thereon, asecond light beam emitting device contained within the housing andlocated adjacent the first light beam emitting device, a second lightposition sensing device contained within the housing and locatedrelative to the second light beam emitting device for receiving thelight beam emitted from the second light beam emitting device andoperable to calculate the position of the light beam received thereonand a refractive optical device located between the second lightemitting device and the second light position sensing device.

The present invention further provides a structural deflection and loadmeasuring device for mounting on a dual wheel axle comprising a housingfor mounting on the axle, at least one mirror assembly for mounting onthe inside of at least one wheel hub cap connected to the wheel axle, atleast one light beam emitting device contained within the housing andoperable to emit at least one light beam towards the mirror assembly, atleast one light position sensing device contained within the housing andlocated adjacent the light beam emitting device having at least twoindependent locations for receiving an incident beam and operable tomeasure the at least two locations. The present invention furtherprovides the device above wherein the at least two independent locationsare located on either the same light sensing device or different lightsensing devices.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will be described in further detailbelow, with reference to the accompanying figures in which:

FIG. 1 is a side view of one embodiment of the optical axle deflectionsensor of the present invention;

FIG. 2 is a side view of the optical axle deflection sensor of FIG. 1shown in a deflected state, with a load applied on the axle;

FIG. 3 is a schematic of the an alternative embodiment of the opticalaxle deflection sensor of the present invention;

FIG. 4 is a side view of the optical deflection sensor of FIG. 1 using aprism to amplify the deflection of the light beam.

FIGS. 5A-C illustrate three separate measurement states for a furtherembodiment of the optical axle deflection sensor of the presentinvention;

FIG. 6 illustrates a further alternative embodiment of the optical axledeflection sensor of the present invention using a reflecting device;

FIG. 7 illustrates an additional embodiment of the optical axledeflection sensor of the present invention including a thermal heaterand cooler element; and

FIGS. 8A and B illustrates a further embodiment of the present inventionfor mounting on a dual wheel axle.

FIG. 9 a is an example of nose landing gear of an aircraft.

FIG. 9 b is an example of main landing gear of an aircraft.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described in further detail withreference to FIGS. 1 through 6. The present invention provides astructural deflection and load measuring device, also referred to hereinas an optical axle deflection sensor or a deflection sensor, having atleast one light beam emitting device and at least one light positionsensing device. The at least one emitting device and the at least onesensing device are mounted on an axle at a spaced apart distance fromeach other. The position of the at least one light beam emitting devicerelative to the at least one sensing device provides that the light beamemitted from the at least one light beam emitting device projects ontothe at least one sensing device when no axle deflection is occurring.Preferably the light beam is projected on to an area of the at least onesensing device at a position that maximises the useful resolution of thesensor. The initial position being chosen when no axle deflection isoccurring. For example, the position of the light beam/dot may be chosento be fairly close to the edge of the sensor for measurements ofweight/vertical force. This position may be chosen since the magnitudeof the loads in the aircraft weight direction are significantly greaterthat the loads in the opposite direction which come mostly from theinertial loading of the wheels, tires, and brakes during free extensionof the shock strut. However, for the fore/aft (drag load) the positionof the light beam/dot may be in the centre.

One embodiment of the present invention will now be described withreference to FIGS. 1 and 2 in which the optical axle deflection sensoris indicated generally at numeral 10. The optical axle deflection sensor10 is mounted to an axle, which is indicated generally at numeral 12.The optical axle deflection sensor 10 uses a light beam emitting device14 and a light position sensing device 16, which may also be referred toas a detector or sensor. The light beam emitting device 14 emits atleast one light beam which is received, in the form of a light image ordot, on a surface of the light position sensing device 16.

When no load is placed on the axle 12 the light beam emitted from theemitting device 14 projects an image or dot onto the centre of thesurface of the sensing device 16. When a load is applied on the axle 12the light beam will deflect relative to the amount of the load and willbe received on the surface of the sensing device at a position thatdiffers from the no load position. The deflection of the light beam maybe very small when lighter loads are applied on the axle relative to thedeflection that occurs when heavy loads are applied.

The light beam emitting device 14 may be any device from which at leastone light beam is emitted. Examples of light beam emitting devices areknown in the art and may be, but are not limited to, for example, alight emitting diode or laser. The light position sensing device 16 maybe any device that is operable to detect, or sense, at least one lightimage received thereon, for example a light dot or a light image orshape, such as a circle or ellipse. Examples of light position sensingdevices are known in the art and may be, but are not limited to, aposition sensitive detectors (PSD) or an optical image sensor such as acharge coupled device (CCD) or complementary metal oxide semiconductor(CMOS) image sensor.

Position-sensitive detectors are photodiodes that are able to detect theposition of a light spot, or dot, projected onto its surface. Theinformation relating to the signal is calculated from the magnitude ofthe photocurrent signals provided on the PSD. Charge coupled devices areintegrated circuits containing an array of linked capacitors which whenhit by light emit electrons which can in turn be measured and used tocalculate the position of the image/dot. The information relating to theposition of the image or dot can then be relayed to a processor orcontrol system that is capable of manipulating this information andcorrelating the change in position of the image/dot, i.e. thedeflection, into information relating to the vertical and drag load onthe axle.

As stated above, the light beam emitting device 14 and the lightposition sensing device 16 are mounted to the axle such that they arespaced apart a distance and aimed at each other such that at nodeflection of the axle the light beam emitted from the emitting deviceprojects a dot, or image, at a position on the sensing device 16. Thelight beam emitting device 14 and the light position sensing device 16are mounted in order that both devices are held at fixed locationsrelative to the axle to ensure that the movement of the axle isreflected, and subsequently measured, in the projection of the lightbeam.

FIG. 3 illustrates one embodiment of the mounting of the sensor 10 tothe axle. In this embodiment the emitting device 14 and the sensingdevice 16 are located within a housing 17 that is mounted within theaxle 12. The housing 17 is attached at peripheral ends to first andsecond rings 19 that are fitted within the internal portion of the axle,through an interference fit. It will be understood that this attachmentis by no means limiting and other ways of attaching the housing 17 tothe internal portion of the axle may be used. For example, the housing17 may include flange portions at either end that can be directlyattached to the internal portion of the axle, for example by welding orusing bolts. Alternatively the housing 17 may be attached to theexternal surface of the axle. The attachment to the external surface maybe through any means already discussed and those known to a personskilled in the art. For example, the housing may be attached atperipheral ends to rings that fit around the external surface of theaxle, i.e. the axle passes through the internal portion of the rings, oralternatively the rings may include flanges or other attachment means bywhich the rings are connected to the axle.

Any load that is applied on the axle 12 will cause a deflection in thebeam that is produced by the light beam emitting device 14, relative toits stationary position when no force is applied to the axle 12. Whenthe beam from the light beam emitting device 14 is deflected, the lightdot, or image, 18 on the sensing device 16 moves proportional to thedeflection. The measurement of the position of the light dot 18, and inparticular of the change in the position of the light dot 18 relative toits stationary position is used to calculate the amount of deflection ofthe axle which in turn allows for the determination of the axle load.

Since the deflection sensor 10 of the present invention may be used todetermine axle loads it will be understood that the deflection sensor 10may therefore be used in any structure on which a load/force is placedthat causes a deflection of the structure relative to its at rest state.For example, and as described herein, the deflection sensor 10 may beused on an aircraft landing gear.

The use of a two dimensional light sensor 10 allows the beam deflectionsto be characterized in two dimensions, i.e. for instance up and down,and fore and aft. When used on an aircraft landing gear, thesedeflections may be correlated to, for example, aircraft vertical load orweight and drag loads, for example from braking.

Depending on the applied load, the relative movement of the light beamemitted from the light beam emitting device 14 compared to the originalstationary, no load, position may be quite small, for example if arelatively small load is applied. Therefore in order to be able tomeasure small movements in the position of the light beam on the lightposition sensing device 16 it may be beneficial to incorporate withinthe sensor 10 an optical device that is capable of amplifying themovement of the light beam.

In a further embodiment, illustrated in FIG. 4, in the deflection sensor10 described above, the light beam emitted from the at least one lightbeam emitting device 14 may therefore be split using optics, such as aprism or a refractive lens, to force the beam to travel a greaterdistance across the light sensing device 16, i.e. to amplify thedeflection. In the embodiment illustrated a prism 20 is connected to theportion of the sensor 10 that includes the light position sensing device16. Examples of other optical devices that may be used are known topersons skilled in the art.

An alternative embodiment is illustrated in FIGS. 5A-C in which theoptical axle deflection sensor 10 includes two light beam emittingdevices 14 and two light position sensing devices 16. The light beamemitting devices 14,14′ are located at one end of the axle 12 and thelight position sensing devices 16,16′ are located at a distance from theemitting devices 14,14′, and close to the opposing end of the axle 12.One of the light beam emitting devices is located at a higher position,referred to as the “upper” device 14′ relative to the second light beamemitting device 14. The upper emitting device 14′ sends a beam on adirect path to one of the detectors 16′ whereas the lower emittingdevice 14 sends a beam that passes through an optical deflection device20, shown in FIG. 5 as a spherical lens, and then onto the seconddetector 16. The optical deflection device 20 may be any optical devicethat provides a magnification of the movement of the light beam, asdiscussed earlier, i.e. a magnification in the increase in the angle ofdeflection of the light beam.

When a large load is applied on the axle 12 the light beam emitted fromthe upper emitting device 14′ will undergo a large deflection which canbe measured by sensing device 16. However, if a small load is appliedthen only a small deflection in the light beam will occur. In thisinstance, the deflection of the light beam emitted from the loweremitting device will be amplified upon passing through the opticaldeflection device 20 and therefore a large deflection may be measured onthe second detector 16.

As discussed above, the deflection sensor may be used on an axle inaircraft landing gear. When the landing gear axle undergoes a largedeflection, as is the case when an aircraft comes in for a landing, thedetector 16′ takes the direct measurements, i.e. not through the opticaldeflection device 20, may be used for the calculation of the light beamdeflection. Axle deflection values in this case may range from 1 to 2mm, which may be an easily detectable distance range for the detector16′ being used. When the landing gear axle 12 undergoes a smalldeflection, as is the case when a plane is stationary on the groundduring loading, the detector 16 takes measurements from the beam thatpasses through the optical deflection device 20. With the smalldeflection, the incident beam coming from the lower emitting device 14moves only a small amount relative to the original position. However,the refracted beam exiting the optical deflection device 20 moves a muchlarger distance against the detector's surface. For example, a 5micrometer movement in the Y direction of the incident beam translatesinto a 500 micrometer movement along the detector's surface. By usingthe optical deflection device 20 to amplify the observed deflection,very small deflections of the axle 12 can be measured.

In a further embodiment, illustrated in FIG. 6, the optical axledeflection sensor 10 may include the use of at least one mirror 26,either plane or having a specific predefined curvature, in order thatthe light beam emitting device 14 and the light position sensing device16 may be placed on the same side of the axle 12. The placement of theemitting device 14 and the point sensing device 16 being on the sameside allow for both devices to be connected to the same electroniccircuit board. The location of the components on the same electroniccircuit board allow for the possibility to maintain all the componentsat the same temperature since they are located within close proximity toeach other. Connection to the same circuit board will also reduce thenumber of wires and power sources that may be required for thecomponents. The use of a mirror, or other reflective device, with aspecific curvature may provide the capability to combine theamplification of deflection function along with the folding of the lightbeam such that the electronics may be mounted together.

In a further embodiment, illustrated in FIG. 7, the optical axledeflection sensor 10 includes at least one heating element 28. Theheating element may be used to either provide heat to the sensor 10 orto cool the sensor 10. The heating element may include at least onethermal heater element 28 and/or at least one cooler element 30. The atleast one thermal heater element 28 may be used to heat the environmentof the sensor components when the sensor is used under extreme coldtemperature conditions. The at least one cooler element 30 may be usedto cool the environment of the sensor components when the sensor 10 isused under extreme heat conditions. The heater and cooler elements 28,30may be separate components or they may be one component having thecapability to provide both hot and cold temperature variations, forexample a Peltier junction may be used to stabilize, under electroniccontrol, the temperature of the emitter and detector. Environments wherelarge variations in temperature occur are, for example, on aircraftlanding gear where severe cold, due to high elevations during flight,and severe heat, due to braking, can occur. The heating and/or coolingelements 28,30 may be used to maintain the sensor 10 at a constanttemperature when in use.

It will be understood that the sensor 10 described above can be used inmany different applications. When used in aircraft landing gear, thesensor 10 may be used to measure weight/balance and therefore may onlybe used during loading of the plane. Alternatively, the sensor 10 may beused for health monitoring purposes, i.e. to monitor the applied loadsplaced on the axle during loading and during landing of the plane. Therequirements for power and monitoring of the sensor 10 in each systemwill therefore vary. For example, if the sensor 10 is only being used tomonitor the weight/balance during loading of the plane then power isonly required for a short pre-determined period of time. The powersource may therefore be supplied through ground control systems or thesensor 10 may be battery powered. In situations where the sensor 10 isbeing used to monitor the health of the aircraft landing gear then powermay be supplied through a connection to the aircraft power system.

The embodiments described above generally refer to a light image or dotlocated on the surface of the point sensing device. The light image maybe any shape that can project onto the surface of the sensing device andthat can be measured by the sensing device to calculate a deflectionfrom the original projected position. Examples of alternative shapesinclude circles that when deflected change shape to form an ellipsewhich indicates a deflection has occurred and the measurement taken canthen be translated into an applied force on the axle. The use of certainimages, for example a cross-like image may reflect torsional movement inthe projected image on the sensing device. Image analysis software maythen be used to correlate the change in image to a torsional force thathas been applied to the axle.

The information obtained by the light position sensing device 16, i.e.the location of the light beam, may be transmitted to an on-boardcontrol system, or processor, for further manipulation or may betemporarily stored in or near the sensor 10 or may be transmitted to aground control system. Systems and methods of relaying such informationinclude the use of processors and transmitters and are known by personsskilled in the art.

The embodiment described above, includes a housing 17 that is used tocontain the at least one light emitting device 14 and the at least onepoint sensing device 16 therein. The housing 17 may be a container whichis closed and then attached by external means to the axle. Alternativelythe housing 17 may be a cover that is positioned over the at least onelight emitting device 14 and the at least one light sensing device 16.In this embodiment the light emitting device 14 is attached directly tothe surface of the axle at a first point and the light sensing device 16is attached directly to the surface of the axle at a second point, withall of the requirements of the positioning of the devices relative toeach other, as described above. The cover may then be placed over thedevice to keep the devices 14,16 protected and to reduce the possibilityof foreign bodies interfering with the light beam projection andmeasurements.

In yet another embodiment, illustrated in FIGS. 8A-B, a sensor package30 is mounted at the midpoint of a dual wheel axle 32. The sensorpackage 30 contains a plurality of light emitting devices 14 and aplurality of light sensing devices 16. The package 30 is installedthrough a hole at the midpoint of the axle such that at least one set oflight emitting devices 14 and light sensing devices 16 face towards oneend of the axle shaft, and at least one other set of light emittingdevices 14 and light sensing devices 16 face towards the other end ofthe axle shaft. By placing the sensor package 30 in such a way that itis insertable through the hole in the axle shaft 32, the sensor package30 may be replaced or repaired in the field. A mirror or mirror and lensassembly 34 is mounted to the inside of the hub cap, not shown, (whichis rigidly attached to the wheel which rotates on the axle). Thismounting arrangement allows for rapid and simple removal and replacementof the components while an aircraft is in service.

In a further embodiment, an additional light emitting device 14 and alight sensing device 16 can be added to the sensor package 30 of theembodiment above, with the additional light emitting device 14 axisoffset from the neutral axis of the axle 32. A plane mirror or otheroptical device 36 mounted to the inside of the hubcap 38, of wheel 40,will have a series of radial strips 42 etched or painted on to reduce oreliminate the reflectivity of the optical device 36. This would causethe light sensing device 16 to receive a series of pulses during wheelrotation that would be proportional to the wheel speed and the number ofstrips (a fixed constant). This system would allow the incorporation ofwheel speed measuring equipment within the axle load detecting system inorder to simplify the equipment currently mounted in an aircraft axle.

The invention will now be described in further detail with regard to theuse of the structural deflection and load measuring device of thepresent invention in an aircraft landing gear. In a typical tricyclearrangement of landing gear there is included a left main landing gearand a right main landing gear and a nose landing gear. An example of theleft/right main landing gear is illustrated in FIG. 9A and an example ofthe nose landing gear is illustrated in FIG. 9B. To achieve a weight andbalance calculation for an aircraft the vertical force acting upon eachaxle is required. The weight of the aircraft is the sum of all thevertical loads and constant weights for the wheels, brakes and tires.

In a cantilever arrangement, the axle remains in a fixed positionrelative to the ground. The axle translates across the ground and itsorientation remains stable. In this type of arrangement a onedimensional axle sensor, as known in the prior art, may be used.However, many landing gear arrangements are of the Bogie or articulatedstyle. In these arrangements the angle that the vertical force acts onthe axle varies with axle position, this is generally even more evidenton an articulated landing gear. One dimensional sensors will thereforenot read the vertical load accurately. However, the two dimensionalsensor device of the present invention is operable to measure this load.

As will be understood by a person skilled in the art, using x and yforce measurements and using the formula Vertical Load =√x²+y² the truevertical load may be measured whenever the aircraft is static.

In a first application used to calculate the weight and balance of anaircraft the system is preferably dual redundant. This means that thesystem includes two light emitting devices and two light sensingdevices. For example, the system may include the light emitting devicesand the light sensing devices located on the same electronics board andpreferably having separate power supplies. In this embodiment, the twolight emitting devices are located in the same plane as the two lightsensing devices and are positioned opposite an optical deflector, e.g. amirror. Alternatively, the system may include two light emitting deviceslocated in the same plane and opposite two light sensing devices. Inboth of these systems the dual light emitting and sensing devices arelocated within one housing. In a system for measuring weight and loadbalance of an aircraft one of the embodiments described above containingthe dual emitting and sensing devices is attached to each axle of theaircraft.

In a second application used to monitor the load on the aircraft it ispreferable to also include a measurement of the side loads. Therefore,in a bogie gear, additional sensor systems, as described above, are alsoincluded in the bogie beam, for example at position A illustrated inFIG. 9B, the measurement axes are indicated at arrows B and C. In acantilever system, additional sensor systems, as described above, may beincluded in the piston.

While this invention has been described with reference to illustrativeembodiments and examples, the description is not intended to beconstrued in a limiting sense. Thus, various modifications of theillustrative embodiments, as well as other embodiments of the invention,will be apparent to persons skilled in the art upon reference to thisdescription. It is therefore contemplated that the appended claims willcover any such modifications or embodiments. Further, all of the claimsare hereby incorporated by reference into the description of thepreferred embodiments.

All publications, patents and patent applications referred to herein areincorporated by reference in their entirety to the same extent as ifeach individual publication, patent or patent application wasspecifically and individually indicated to be incorporated by referencein its entirety.

1. A structural deflection and load measuring device for mounting on anaxle comprising: (i) at least one light beam emitting device connectedto the axle and operable to emit at least one light beam; and (ii) atleast one light position sensing device connected to the axle andlocated relative to the light beam emitting device, the at least onelight position sensing device comprising at least two independentlocations for receiving an incident beam and operable to measure the atleast two independent locations.
 2. The structural deflection and loadmeasuring device according to claim 1, wherein the one of the at leasttwo locations is located on a first light position sensing device andthe other is located on a second light position sensing device.
 3. Thestructural deflection and load measuring device according to claim 1,comprising a plurality of light position sensing devices wherein the atleast two independent locations for receiving an incident beam arelocated on different light position sensing devices.
 4. The structuraldeflection and load measuring device according to claim 1, furthercomprising a refractive optical device located between the at least onelight position sensing device and the at least one light emitting deviceand within the path of the light beam.
 5. The structural deflection andload measuring device according to claim 1, wherein the at least onelight beam emitting device and the at least one light position sensingdevice are located proximal to each other and the sensor furthercomprises a reflective optical device located at a position distal fromthe at least one light beam emitting device and the at least one lightposition sensing device and positioned to reflect the beam emitted fromthe at least one emitting device onto the at least one position sensingdevice.
 6. The structural deflection and load measuring device accordingto claim 1, further comprising at least one of at least one heatingelement and at least one cooling element.
 7. The structural deflectionand load measuring device according to claim 1, further comprising ahousing for mounting on the axle, the housing being operable to containthe at least one light beam emitting device and the at least one lightposition sensing device therein.
 8. The structural deflection and loadmeasuring device according to claim 7, wherein the housing is mounted onthe axle.
 9. The structural deflection and load measuring deviceaccording to claim 1, further comprising a second light beam emittingdevice connected to the axle and operable to emit at least one lightbeam, a second light position sensing device connected to the axle andlocated relative to the second light beam emitting device for receivingat least one light beam emitted from the second light beam emittingdevice thereon, and a refractive optical device located between thesecond light emitting device and the second light position sensingdevice.
 10. The structural deflection and load measuring deviceaccording to claim 1, further comprising transmitting means connected tothe at least one light position sensing device for transmitting thecalculated position of the light beam.
 11. The structural deflection andload measuring device according to claim 10, further comprising aprocessor connected to the transmitting means and operable to calculateat least one of weight, balance and load of the aircraft using thecalculated position of the light beam.
 12. A method for measuring axledeflection using an optical axle deflection sensor comprising at leastone light emitting device connected to the axle and at least one lightposition sensing device connected to the axle and located relative tothe light beam emitting device for receiving at least one light beamfrom the light beam emitting device thereon, the method comprising thesteps of: (i) measuring the position of the light beam from the lightbeam emitting device on the light position sensing device when no loadis applied to the axle; (ii) applying a load to the axle andre-measuring the position of the light beam on the sensing device; (iii)comparing the position of the light beam in (i) with (ii) andcalculating the light beam deflection; and (iv) calculating the axledeflection using the light beam deflection calculated in (iii).
 13. Themethod of claim 12, further comprising using the calculated axledeflection of step (iv) to determine at least one of weight, balance andload on the axle.
 14. A structural deflection and load measuring devicefor mounting on a dual wheel axle comprising: (i) a housing for mountingon the axle; (ii) at least one mirror assembly for mounting on theinside of at least one wheel hub cap connected to the wheel axle; (iii)at least one light beam emitting device contained within the housing andoperable to emit at least one light beam towards the mirror assembly;(iv) at least one light position sensing device contained within thehousing and located adjacent the light beam emitting device forreceiving the at least one deflected light beam from the mirror assemblythereon and operable to calculate the position of the light beamreceived thereon.
 15. The structural deflection and load measuringdevice according to claim 12, wherein the mirror assembly comprises aplurality of light absorbing elements thereon.
 16. The structuraldeflection and load measuring device according to claim 13, wherein theplurality of light absorbing elements are radially extending elements.17. The structural deflection and load measuring device according toclaim 13, wherein the mirror assembly comprises at least one mirror andat least one of a reflective lens and a refractive lens.
 18. Thestructural deflection and load measuring device according to claim 12,further comprising transmitting means connected to the at least onelight position sensing device for transmitting the calculated positionof the light beam.
 19. The structural deflection and load measuringdevice according to claim 16, further comprising a processing connectedto the transmitting means and operable to calculate at least one ofweight, balance and load of the aircraft using the calculated positionof the light beam.
 20. A system for measuring the weight, balance and/orload of an aircraft comprising at least one structural deflection andload measuring device according to claim 1 located on each axle of theaircraft.
 21. the system according to claim 15, further comprisingadditional structural deflection and load measuring devices mounted atpredetermined positions on the aircraft landing gear.
 22. A structuraldeflection and load measuring device for mounting on an axle comprising:a housing for mounting on the axle; a first light beam emitting devicecontained within the housing and operable to emit at least one lightbeam; a first light position sensing device contained within the housingand located relative to the light beam emitting device for receiving atleast one light beam from the first light beam emitting device thereonand operable to calculate the position of the light beam receivedthereon; a second light beam emitting device contained within thehousing and located adjacent the first light beam emitting device; asecond light position sensing device contained within the housing andlocated relating to the second light beam emitting device for receivingthe light beam emitted from the second light beam emitting device andoperable to calculate the position of the light beam received thereon;and a refractive optical device located between light emitting deviceand the second light position sensing device.
 23. The structuraldeflection and load measuring device according to claim 20, furthercomprising at least one transmitting device for transmitting thecalculated positions of the first and second light beams on respectivefirst and second light beam sensing devices.
 24. A structural deflectionand load measuring device for mounting on a dual wheel axle comprising:(i) a housing for mounting on the axle; (ii) at least one mirrorassembly for mounting on the inside of at least one wheel hub capconnected to the wheel axle; (iii) at least one light beam emittingdevice contained within the housing and operable to emit at least onelight beam towards the mirror assembly; (iv) at least one light positionsensing device contained within the housing and located adjacent thelight beam emitting device having at least two independent locations forreceiving an incident beam and operable to measure the at least twolocations.
 25. The structural deflection and load measuring deviceaccording to claim 24, wherein the device comprises a plurality of lightposition sensing devices and the at least two independent locations arelocated on separate light position sensing devices.
 26. The structuraldeflection and load measuring device according to claim 24, wherein theat least two independent locations are located on the same lightposition sensing device.
 27. The structural deflection and loadmeasuring device according to claim 24, wherein the mirror assemblycomprises a plurality of light absorbing elements thereon.
 28. Thestructural deflection and load measuring device according to claim 27,wherein the plurality of light absorbing elements are radially extendingelements.
 29. the structural deflection and load measuring deviceaccording to claim 24, wherein the mirror assembly comprises at leastone mirror and at least one of a reflective lens and a refractive lens.30. the structural deflection and load measuring device according toclaim 24, further comprising transmitting means connected to the atleast one light position sensing device for transmitting the position ofthe at least two independent locations.
 31. The structural deflectionand load measuring device according to claim 30, further comprising aprocessor connected to the transmitting means and operable to calculateat least one of weight, balance and load of the aircraft using thetransmitted position of the at least two independent locations.